1. Field of the Invention
The present invention provides a method of generating discharge plasma.
2. Related Art Statement
According to Japanese patent publication No. 2004-270022A, a nano-pulse electric power source having a pulse width of 1000 nsec or smaller is used to form a diamond-like carbon film under atmospheric pressure.
Japanese patent publication No. H09-312280A disclosed that pulse discharge is maintained at an off-time of pulse discharge of 0.5 μs to 30 μs. The duty ratio of the pulse voltage is as large as 10 percent or higher and so-called microwave (high frequency wave of 2.45 GHz) is converted to pulse wave.
According to Japanese patent No. 3705977B, the modulation period is made 10 to 500 μs and the duty ratio is made 10 to 80 percent. Also according to this method, as a source for generating plasma, high frequency wave of 0.4 to 13.56 MHz is converted to pulse wave for use in etching process.
According to Japanese patent publication No. 2005-159049A, the repetition period of high frequency is made 10 to 100 kHz and the duty ratio is made 40 to 60 percent for generating plasma for use in film formation.
Japanese patent publication No. 2000-124190A disclosed a plasma source having an electron temperature of 0.25 to 1 eV utilizing microwave (0.3 to 1 GHz) as the plasma source.
According to Japanese patent No. 3639795A, pulses having different polarities are superimposed to supply electric power to obtain plasma having an electric temperature of 3 eV or lower and density of 2×108 cm−3 or lower. The off-time of the pulse is not, however, controlled and the electron density is very low.